Light exposure is known to mediate an increase in retinoic acid, a key regulator of many biological functions, in the neural retina and retinal pigment epithelium(RPE). In the adult eye, the retinal pigment epithelium ( RPE) is the principal site of synthesis of retinoic acid, a key regulator of many biological functions through its nuclear receptors, RARs and RXRs. Light exposure is known to mediate an increase in retinoic acid, a key regulator of many biological functions, in the neural retina and retinal pigment epithelium(RPE). In the adult eye, the retinal pigment epithelium ( RPE) is the principal site of synthesis of retinoic acid, a key regulator of many biological functions through its nuclear receptors, RARs and RXRs. We have shown that the retinoid receptors, RARa and RXRa, are present in the well characterized human RPE cell line, ARPE-19, and we are focusing on the regulation by retinoic acid of genes expressed in the RPE. We have characterized NORPEG, a novel gene present in ARPE-19 cells where its expression is regulated by retinoic acid. The NORPEG gene encodes a protein containing 980 amino acid residues. The ~110 kDa protein was transiently expressed in COS-7 cells as a FLAG fusion protein and was immunolocalized to the cytoplasm. Confocal microscopic analysis of the NORPEG protein in ARPE-19 cells showed threadlike projections in the cytoplasm reminiscent of the cytoskeleton. Consistent with this localization, the expressed NORPEG protein showed resistance to solubilization by Triton X-100 and KCL. We have characterized an ortholog of NORPEG from the mouse, and its expression, when analyzed by in situ hybridization, appears to be developmentally regulated. We have used differential display analysis to identify several other genes expressed in RPE cells whose expression is regulated by retinoic acid. One of these genes was characterized as Stearoyl-CoA desaturase (SCD), a key regulatory enzyme in the lipid metabolic pathway. A marked increase in SCD message following retinoic acid treatment was observed in both ARPE-19 and D407 cell lines. In addition, SCD mRNA in cultured RPE cells is greatly induced by TGF-b.